Physics question

[123dental]

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Here's a physics question that I am getting a bit confused by...what do you guys think that the answer would be?

A boat loaded with rocks is floating in a swimming pool. If the rocks are thrown into the water and settle on the bottom of the pool, the water level in the pool:
a) falls
b) stays the same
c) there is not enough info to answer the question

Thanks

 

[cjmetcalf7883]

I believe the answer is B because the weight is displacing the water in the pool, if you put the rocks back into the water the water level will not change BUT the position of the boat in the water will.

 

[gochi]

Here's a physics question that I am getting a bit confused by...what do you guys think that the answer would be?

A boat loaded with rocks is floating in a swimming pool. If the rocks are thrown into the water and settle on the bottom of the pool, the water level in the pool:
a) falls
b) stays the same
c) there is not enough info to answer the question

Thanks

B- you're not adding anything to the system, i.e its a closed system therefore nothing will change. If you were to through in a dense box per say then the level will rise since you have introduced an external object. If you were to remove the rocks from the boat into the water the overall mass off the system would still be the same, so h20 level should not increase/decrease.

BTW, is this an OAT question ? Im wondering since there's a 33% chance you could guess the correct answer...

 

[daisy497]

The answer is actually A. It falls.
Consider the volume of water caused to be displaced by the rocks before and after they are thrown out.

 

[zyg0te]

The answer is actually A. It falls.
Consider the volume of water caused to be displaced by the rocks before and after they are thrown out.

This is correct.

 

[mathcod]

The floating boat with rocks puts more pressure on the water, causing the water level to rise. But on the other hand, the rocks in the water displaces water and pushes it higher. Don't we have to consider both facts? We don't know the mass or density of the rocks (except they're denser than water) nor their size.

Is the answer C, 123Dental?

 

[mathcod]

I also want to just say that I like how most everyone offered their reasoning why their answer was correct. It's interesting to see how we think and helps the discussion. Posters chose each of the possible answers, I dunno but I find it really cool how people think.

 

[zyg0te]

The floating boat with rocks puts more pressure on the water, causing the water level to rise. But on the other hand, the rocks in the water displaces water and pushes it higher. Don't we have to consider both facts? We don't know the mass or density of the rocks (except they're denser than water) nor their size.

Is the answer C, 123Dental?

It is A without a doubt.
The key thing is the rock is more dense than water (it sinks).
Denisty = mass/volume

Say the rocks weighs 1kg. While it is in a floating boat, it displaces 1kg of water (1L). However, when that rock is thrown in the water, it will displace less water(example: 0.8L).

In other words, displacing 1kg of water is more than displacing 1kg of rock.

 

[sportsdude00]

It is A without a doubt.
The key thing is the rock is more dense than water (it sinks).
Denisty = mass/volume

Say the rocks weighs 1kg. While it is in a floating boat, it displaces 1kg of water (1L). However, when that rock is thrown in the water, it will displace less water(example: 0.8L).

In other words, displacing 1kg of water is more than displacing 1kg of rock.

I agree. The water would only remain if the two densities are equal

 

[sportsdude00]

From my experience with questions like these, the answer is not usually the one that is equal or the same. Most of the time when you're answering this type of question, you think about the ideal case (here, densities are equal) first, and they want to see if you can analyze a specific situation based on that case. Sometimes the answer is the "equal" choice though, and I know I over analyze those questions a lot...